1. Field of the Invention
The present invention relates to a thin film magnetic head using a giant magnetoresistive effect and, more particularly, to a thin film magnetic head constructed so that current is passed in a stacking direction in a magnetoresistive effect film and a method of manufacturing the same.
2. Description of the Related Art
Hitherto, for reproducing information on a magnetic recording medium such as a hard disk, a thin film magnetic head having an MR element displaying a magnetoresistive (MR) effect is widely used. In resent years, recording density of a magnetic recording medium is increasing, and a thin film magnetic head using a giant magnetoresistive effect element (GMR element) displaying a giant magnetoresistive (GMR) effect is generally used. An example of the GMR elements is a spin valve (SV) type GMR element.
The SV-type GMR element includes an SV film having a structure in which a magnetic layer whose magnetization direction is pinned and a magnetic layer whose magnetization direction changes according to a signal magnetic field from the outside are stacked via a nonmagnetic layer, and is constructed so that sense current flows in a multilayer in-plane direction at the time of reproducing operation. Such a GMR element is particularly called a CIP (Current in Plane)-GMR element. In this case, electric resistance of the sense current changes according to relative angles of the magnetization directions in the two magnetic layers of the SV film.
Recently, to adapt to further improvement in recording density, a thin film magnetic head having a tunnel magnetoresistance (TMR) effect element using tunnel current flowing in a very thin insulating layer is being developed. The TMR element includes a TMR film of a structure in which a very thin insulating layer is provided between two magnetic layers and is constructed so that sense current flows in the stacking direction in reproducing operation. In this case, electric resistance at the time of passage of the tunnel current through the very thin insulating layer changes according to a signal magnetic field from the outside.
On the other hand, like the TMR element, a thin film magnetic head having a CPP (Current Perpendicular to the Plane)-GMR element constructed so that sense current flows in the stacking direction is also being developed (refer to, for example, “Journal of Applied Physics”, Vol. 89, No. 11, p. 6943, 2001 (non-patent document 1)). FIG. 20 shows an example of a sectional configuration of such a conventional CPP-GMR element (MR element 110). FIG. 20 is a cross section seen from a recording medium facing surface which faces a magnetic recording medium from which information is read. As shown in FIG. 20, the MR element 110 has an SV film 120 which is a metal multilayer film, a pair of magnetic domain control films 112 disposed so as to face each other while sandwiching the SV film 120 in a direction (X direction) corresponding to the recording track width direction, and a lower shield layer 111 and an upper shield layer 114 formed so as to sandwich the SV film 120 and the pair of magnetic domain control films 112 in the stacking direction (Z direction). A pair of insulating layers 115 are formed between the SV film 120 and the pair of magnetic domain control films 112. Further, a pair of insulating layers 113 are formed between the upper shield layer 114 and the pair of magnetic domain control films 112. The SV film 120 has, in order from the side of the lower shield layer 111, an under layer 131, an antiferromagnetic layer 132, a magnetization direction pinned layer 133, a magnetic sensitive layer 134, and a protection layer 135. The magnetization direction pinned layer 133 has a three-layer structure in which a nonmagnetic layer 133B is formed between two ferromagnetic layers 133A and 133C and its magnetization direction is pinned by the antiferromagnetic layer 132. The magnetic sensitive layer 134 has a three-layer structure in which a ferromagnetic layer 134B is formed between two non-magnetic layers 134A and 134C. The pair of magnetic domain control films 112 act on the ferromagnetic layer 134B so that the ferromagnetic layer 134B is formed as a single magnetic domain.
The CPP-GMR element as shown in FIG. 20 has advantages such that resistance is lower as compared with that of the TMR element and a higher output can be obtained as compared with an output of a CIP-GMR element even in the case where a track width is very narrow. Concretely, in the TMR element, a tunnel barrier layer has to have a certain degree of thickness from the viewpoint of manufacturing or the like, and a sufficiently small resistance value R is not obtained. On the other hand, in the CIP-GMR element, sense current is passed in the in-plane direction. Therefore, as the width in the direction corresponding to the recording track width direction decreases, a magnetic sensitive part through which the sense current passes is very narrowed, and a resistance change amount ΔR decreases. In the CPP-GMR element, however, the sense current is passed in the stacking direction, so that an influence on the resistance charge amount ΔR exerted by reduction in the recording track width direction is small. Different from the TMR element, an insulating material is not included as an element of the SV film, so that the resistance value R is small. From such background, expectation for the CPP-GMR element is increasing as an element capable of adapting to further improvement in recording density. For example, in the CPP-GMR element described in Japanese Unexamined Patent Publication No. 2002-329905 (patent document 1), the width of a portion including a magnetic sensitive layer in the GMR film is further reduced, and a narrower effective core width is realized.
In the CPP-GMR element described in the patent document 1, however, an insulator is provided between a portion (upper layer member) including the magnetic sensitive layer in the SV film and a magnetic domain control film. Due to this, contribution of a vertical bias magnetic field to the magnetic sensitive layer is insufficient, and it is concerned that a single magnetic domain is not sufficiently formed. Specifically, in the configuration of the patent document 1, the distance between the magnetic sensitive layer and the magnetic domain control film is long, so that a magnetic flux generated by the magnetic domain control film passes mainly upper and lower shield layers, not the magnetic sensitive layer. It is considered that a sufficient vertical bias magnetic field is not applied to the magnetic sensitive layer.
Further, in the CPP-GMR element, the resistance value of a portion which does not contribute so much to the resistance change amount ΔR is larger than the resistance value of a portion largely contributing to the resistance change amount ΔR. Therefore, only a relatively low magnetic resistance change rate (also called MR ratio) ΔR/R is obtained, so that improvements are being demanded. Since the upper and lower shield layers (a lower shield layer 111 and an upper shield layer 114 in FIG. 20) also have a function of lead layers for passing current to the SV film, the CPP-GMR element is inherently advantageous to achieve higher recording density more than the CIP-GMR element separately requiring a lead layer. For example, in the conventional CPP-GMR element as shown in FIG. 20, however, both ends of a top surface 120U (a boundary surface with the upper shield layer 114) of the SV film 120 are partially covered with the insulating layer 113, and the top surface 113U (a boundary surface with the upper shield layer 114) is swollen to the side of the upper shield layer 114, so that a gap G is formed in the Z direction. Consequently, a shield effect of the upper shield layer 114 is weakened, and it is considered to be a factor of disturbing increase in packing density.